The device of the present invention is an improvement over that disclosed in U.S. Pat. No. 3,903,810. The device in said patent operates satisfactorily for the purposes disclosed therein. I have analyzed the device disclosed in said patent and have made various improvements. If there is a power failure, the device disclosed in said patent will permit all vehicles to bypass the control device since the device may be in an inoperative position. This is an undesirable feature and is solved by the present invention wherein the control device is in an operative position for stopping all vehicles in the event of an power failure while at the same time having other advantages over the device disclosed in said patent.